A pulley is a wheel on an axle to support movement of a cable or belt along its circumference. Pulleys are used to lift loads, apply forces, and to transmit power. In short, pulleys help in lifting and moving things from one stationary place to another using a rope. Pulleys are driven by a rope, cable, belt or chain. Pulleys are used in most mechanical gadgets like engine, gear system, belt drive, etc. Pulleys play an important role in speed reduction and increase. Examples of pulleys include flag poles, cranes, water pumps, air conditioners, automobile engines, etc.